This invention relates to an ignition timing control system for an internal combustion engine.
The ignition timing of internal combustion engines is controlled so as to maximize the efficiency of the engine with respect to the mode of operation thereof. It is generally desirable to control the ignition timing so that the particular internal combustion engine approaches a minimum advance for the best torque which may be abbreviated to "MBT" as close as possible within the range in which knocking is not caused in the engine. However, ignition timing control systems previously provided on internal combustion engines have been, in many cases, of the mechanical type and the ignition advance angle characteristics thereof have not been stable with respect to deviations of dimensions and secular changes of components involved. Therefore, the ignition timing has been actually controlled to retard substantially behind an ignition time point giving the desirable advance angle characteristic in order to prevent the occurrence of knocking. In this case the engine deteriorates in efficiency. Also even when ignition timing control systems free from both deviations of dimensions and secular changes as described above are employed, knocking occurring in an associated internal combustion engine depends upon an inlet air temperature and an inlet humidity of the engine and further upon an air fuel ratio thereof, etc. Accordingly, if the ignition timing could be controlled so as not to cause knocking in the engine in some mode of operation, there might be a fear that knocking would be caused in the engine in another mode of operation.
Therefore by sensing knocking and controlling the ignition timing to retard upon the occurrence of knocking, the ignition timing can be adjusted so that knocking is scarcely caused even though an error would occur in the ignition advance angle characteristic due to the deviations as described above of mechanical aparatus and differences between the modes of operation. When internal combustion engines are operated in the steady state or when they are slowly accelerated or decelerated, the engines do not sharply vary in the operating conditions and therefore knocking can be stably controlled. However, upon the rapid acceleration of the engines, the air fuel ratio and the ignition time point are rapidly and substantially changed. Accordingly extreme knocking is apt to be extremely caused in the engines and the intensity of knocking become very high. As a result, it has been difficult to suppress quickly knocking by means of the conventional control.
Accordingly, it is an object of the present invention to provide a new and improved ginition timing control system for controlling ignition timing of an internal combustion engine in accordance with a knock signal originating from the engine so that, upon the rapid acceleration of the engine, a retard angle for the knocking control is increased, thereby to suppress knocking quickly.